Kin selection in density regulated populations.

The process of kin selection has both intra- and inter-group components (Hamilton, 1975, in: Biosocial Anthropology Wade, 1980). Group advantageous characteristics can evolve when inter-group differences in fertility are sufficiently great to overcome any within-group disadvantage of the trait. The potential magnitude of inter-group differences in fertility is determined largely by the way a population is regulated. Inter-group differences decrease as the spatial scale over which a population is regulated becomes increasingly localized. The present paper extends previous work by Boyd (1982, Anim. Behav. 30, 972-982) on the quantitative relation between kin selection and density regulation. A simple genetic model is employed to examine the conditions under which the interaction of local density regulation and kin selection can maintain a stable polymorphism. The ecological factors determining the spatial and temporal scale of density regulation are discussed. Finally, the results are applied to two biological cases in which local density regulation may be influencing the direction of phenotypic plasticity in group advantageous characters.